Multi-functional linear siloxane compound, a siloxane polymer prepared from the compound, and a process for forming a dielectric film by using the polymer

ABSTRACT

A novel multi-functional linear siloxane compound, a siloxane polymer prepared from the siloxane compound, and a process for forming a dielectric film by using the siloxane polymer. The linear siloxane polymer has enhanced mechanical properties (e.g., modulus), superior thermal stability, a low carbon content and a low hygroscopicity and is prepared by the homopolymerization of the linear siloxane compound or the copolymerization of the linear siloxane compound with another monomer. A dielectric film can be produced by heat-curing a coating solution containing the siloxane polymer which is highly reactive. The siloxane polymer prepared from the siloxane compound not only has satisfactory mechanical properties, thermal stability and crack resistance, but also exhibits a low hygroscopicity and excellent compatibility with pore-forming materials, which leads to a low dielectric constant. Furthermore, the siloxane polymer retains a relatively low carbon content but a high SiO 2  content, resulting in its improved applicability to semiconductor devices. Therefore, the siloxane polymer is advantageously used as a material for dielectric films of semiconductor devices.

BACKGROUND OF THE INVENTION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Korean Patent Application No. 2003-90909 filed on Dec. 13,2003, which is herein incorporated by reference.

1. Field of the Invention

The present invention relates to a novel multi-functional linearsiloxane compound, a siloxane polymer prepared from the siloxanecompound, and a process for forming a dielectric film by using thesiloxane polymer. More particularly, the present invention relates to anovel multi-functional linear siloxane compound which can be changedinto a polymer having advantageous mechanical properties, e.g., modulus,superior thermal stability, a low carbon content and a lowhygroscopicity; a siloxane polymer prepared by the homopolymerization ofthe linear siloxane compound or the copolymerization of the linearsiloxane compound with another monomer; and a process for forming adielectric film which comprises the step of heat-curing a coatingsolution containing the siloxane polymer.

2. Description of the Related Art

In recent years, as the integration density of semiconductor integratedcircuits has increased, the transmission of electric signals betweenwirings has slowed due to an increased RC delay. For this reason, thereis a growing interest in lowering the capacitance of interlayerinsulating thin films for semiconductor devices. For example, U.S. Pat.Nos. 3,615,272, 4,399,266, 4,756,977 and 4,999,397 disclosepolysilsesquioxane dielectric films having a dielectric constant ofabout 2.5˜3.1 which can be formed by spin-on-deposition (SOD). Thepolysilsesquioxane dielectric films can replace conventional SiO₂dielectric films which have a dielectric constant of about 4.0), formedby chemical vapor deposition (CVD). On the other hand, hydrogensilsesquioxanes and a number of preparation processes thereof are wellknown in the art. For example, U.S. Pat. No. 3,615,272 teaches a processfor preparing a completely condensed hydrogen silsesquioxane bycondensing trichloro-, trimethoxy- or triacetoxysilane in a sulfuricacid medium. Further, U.S. Pat. No. 5,010,159 discloses a process forpreparing a hydrogen silsesquioxane by hydrolyzing a hydridosilane in anarylsulfonic acid hydrate-containing hydrolysis medium to form a resin,and contacting the resin with a neutralizing agent. Further, U.S. Pat.No. 6,232,424 suggests a highly soluble silicone resin compositionhaving excellent solution stability which is prepared by hydrolyzing andcondensing a tetraalkoxysilane, an organosilane and anorganotrialkoxysilane in the presence of water and a catalyst. U.S. Pat.No. 6,000,339 reports a process for preparing a silica-based compoundwhich has improved oxygen plasma resistance and other physicalproperties, and enables the formation of a thick-layer. According tothis process, the silica-based compound is prepared by reacting amonomer selected from alkoxysilanes, fluorine-containing alkoxysilanesand alkylalkoxysilanes with an alkoxide of titanium (Ti) or zirconium(Zr) in the presence of water and a catalyst. U.S. Pat. No. 5,853,808discloses siloxane and silsesquioxane polymers useful for preparingSiO₂-rich thin films wherein the polymers are prepared fromorganosilanes having a β-substituted reactive group, and the thin filmcompositions containing these polymers. Also, alkoxysilane compositionsand insulating thin films formed by using these compositions aredescribed in EP 0 997 497 A1. These compositions are obtained byhydrolyzing and condensing a mixture of at least one alkoxysilaneselected from monoalkoxysilanes, dialkoxysilanes, trialkoxysilanes,tetraalkoxysilanes and trialkoxysilane dimers. In addition, U.S. Pat.No. 5,378,790 discloses organic/inorganic hybrid materials havingexcellent physical properties. Korean Patent No. 343938 discloses asiloxane composition prepared by hydrolyzing and condensing a cyclicsiloxane monomer, and a dielectric thin film formed by using thiscomposition.

However, dielectric thin films formed by using the siloxane polymersprepared from the prior art have the problem of an insufficiently lowdielectric constant. Because they have a low dielectric constant, theypossess poor mechanical properties. Additionally, they exhibit a limitedapplicability to semiconductor processes due to a high organic carboncontent. In particular, in the case of a polymer prepared from a“Q”-shaped Si compound such as tetramethoxysilane, there is the problemof a high hygroscopicity, despite a low organic carbon content and goodmechanical properties in the dielectric films, causing a drasticincrease in the dielectric constant. Accordingly, the polymer haslimited applicability to dielectric films, particularly those formed bythe SOD process. In recent years, there has been an increased demand forcombining siloxane polymers highly compatible with pore-formingmaterials so as to create a lower dielectric constant.

Thus, there is a need in the art to develop a material for forming adielectric film by the SOD process which has a low dielectric constant,superior mechanical properties, e.g., modulus, excellent compatibilitywith pore-forming material, and markedly improved applicability tosemiconductor processes, due to a low carbon content.

SUMMARY OF THE INVENTION

Research has been intensively conducted to solve the above-mentionedproblems. As a result, the present inventors have found that amulti-functional linear siloxane compound with a particular structure isexcellent in reactivity, and if necessary, can be easily formed into aladder structure when polymerized. The present inventors have also foundthat a siloxane polymer prepared by the homopolymerization of themulti-functional linear siloxane compound, or the copolymerization ofthe siloxane compound with another siloxane- or silane-based monomer,exhibits excellent mechanical properties, thermal stability and crackresistance, is highly compatible with conventional pore-formingmaterials, and maintains its hygroscopicity at a low level even duringthe SOD process, thus ensuring excellent insulating characteristics, andretaining a relatively low carbon content but a high SiO₂ content,resulting in an improved applicability to semiconductor processes. Thepresent invention is based on these findings.

Therefore, it is a feature of the present invention to provide amulti-functional siloxane compound which can impart excellent mechanicalproperties, thermal stability, insulating properties and crackresistance to a dielectric film.

It is another feature of the present invention to provide a siloxanepolymer or copolymer prepared from the multi-functional siloxanecompound.

It is yet another feature of the present invention to provide a processfor forming a dielectric film by using the siloxane polymer orcopolymer.

In accordance with the features of the present invention, there isprovided a multi-functional linear siloxane compound represented byFormula 1 below:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are each independently ahydrogen atom, a C₁₋₃ alkyl group, a C₃₋₁₀ cycloalkyl group, a C₂₋₃alkenyl group, a C₆₋₁₅ aryl group, a C₁₋₁₀ alkoxy group, a C₁₋₁₀ acyloxygroup, a C₁₋₁₀ silyloxy group or a halogen atom, at least one of thesesubstituents is a hydrolysable functional group; M is an oxygen atom ora C₁₋₃ alkylene group; n is an integer between 1 and 20; and A is anoxygen atom or a C₁₋₃ alkylene group, at least one A is different fromM, provided that when n is 2 or more, each A is the same or different.

In accordance with the features of the present invention, there isfurther provided a siloxane polymer which is prepared by the hydrolysisand polycondensation of the multi-functional linear siloxane compound inan organic solvent in the presence of water and an acid or basecatalyst.

In accordance with the features of the present invention, there isfurther provided a siloxane copolymer which is prepared by thehydrolysis and polycondensation of the multi-functional linear siloxanecompound with another siloxane- or silane-based monomer, in an organicsolvent in the presence of water and an acid or base catalyst.

In accordance with the features of the present invention, there is yetfurther provided a process for forming a dielectric film by using thesiloxane polymer or copolymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be explained in more detail.

Multi-Functional Linear Siloxane Compound

The linear siloxane compound of Formula 1 according to the presentinvention may have a plurality of reactive groups according to theintended purpose, and thus facilitates the formation into a ladderstructure depending on its structure when polymerized. Accordingly, thepolymer can exhibit excellent mechanical properties (e.g., hightoughness and modulus) because of its ladder structure. Appropriatechoice of M and A in Formula 1 causes a substantial reduction in carboncontent, a decrease in CTE (coefficient of thermal expansion) andconsiderable reduction in the content of alkoxy groups in the polymersto be prepared, thereby enabling the preparation of polymers almostdevoid of moisture absorption.

Preferred linear siloxane compounds of the present invention are thoserepresented by Formulae 2 to 4 below:

wherein M′ is a C₁₋₃ alkylene group; R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉and R₁₀ are each independently a hydrogen atom, a C₁₋₃ alkyl group, aC₃₋₁₀ cycloalkyl group, a C₂₋₃ alkenyl group, a C₆₋₁₅ aryl group, aC₁₋₁₀ alkoxy group, a C₁₋₁₀ acyloxy group, a C₁₋₁₀ silyloxy group or ahalogen atom, at least three of these substituents are hydrolysablefunctional groups; and n is an integer between 1 and 20;

wherein M′, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈ and n are as defined inFormula 2; and

wherein M′, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀ and n are as definedin Formula 2.

More preferably, the multi-functional linear siloxane compound of thepresent invention is represented by any one of Formulae 5 to 7 below:

Polymers prepared from “Q”-shaped Si compounds generally exhibitexcellent mechanical properties, but involve an increase in dielectricconstant due to their high hygroscopicity. In contrast, although thelinear siloxane compound of the present invention, (e.g., the compoundof Formula 7) may have a “Q”-shaped structure incorporated in thebackbone chain, it can maintain the hygroscopicity at a very low level,which leads to superior insulating characteristics, and has goodcompatibility with conventional pore-forming materials and excellentmechanical properties.

The linear siloxane compound of the present invention can be preparedthrough suitable synthetic pathways depending on its structure. Forinstance, the compounds of Formulae 5 to 7 can be prepared in accordancewith Reaction Schemes 1 to 3 below:

Siloxane Polymer

Additionally, the present invention provides a siloxane polymer preparedby the polymerization of the multi-functional linear siloxane compound,optionally with at least one monomer selected from compounds representedby Formulae 8 to 11 below:

wherein R₁ is a hydrogen atom, a C₁₋₃ alkyl group, a C₁₋₃ alkoxy groupor a C₆₋₁₅ aryl group; R₂ is a hydrogen atom, a C₁₋₁₀ alkyl group orSiX₁X₂X₃ (in which X₁, X₂ and X₃ are each independently a hydrogen atom,a C₁₋₃ alkyl group, a C₁₋₁₀ alkoxy group or a halogen atom, at least oneof these substituents is a hydrolysable functional group); and p is aninteger between 3 and 8;

wherein R₁ is a hydrogen atom, a C₁₋₃ alkyl group or a C₆₋₁₅ aryl group;X₁, X₂ and X₃ are each independently a hydrogen atom, a C₁₋₃ alkylgroup, a C₁₋₁₀ alkoxy group or a halogen atom, at least one of thesesubstituents is a hydrolysable functional group; m is an integer between0 and 10; and p is an integer between 3 and 8; and

Formula 10X₃X₂X₁Si-M-SiX₁X₂X₃

wherein X₁, X₂ and X₃ are each independently a hydrogen atom, a C₁₋₃alkyl group, a C₁₋₁₀ alkoxy group or a halogen atom, at least one ofthese substituents is a hydrolysable functional group; M is a C₁₋₁₀alkylene or C₆₋₁₅ arylene group; and

Formula 11(A′)_(n)Si(B′)_(4-n)

wherein A′ is a hydrogen atom, a C₁₋₃ alkyl group or a C₆₋₁₅ aryl group,provided that when n is 2 or more, each A′ is the same or different; B′is a hydroxyl, halogen, C₁₋₃ alkoxy or C₆₋₁₅ aryloxy group, providedthat when n is 2 or less, each B′ is the same or different; and n is aninteger between 0 and 3, in an organic solvent in the presence of anacid or base catalyst.

Preferred compounds of Formula 8 which can be used in the presentinvention are TS-T4 (OH), TS-T4 (OMe), TS-T4Q4, TS-T4T4 and TS-Q4 below:

A preferred example of the compound of Formula 9 is TCS-2 below:

A preferred example of the compound of Formula 10 is BTMSE:

Preferred compounds of Formula 11 which can be used in the presentinvention are MTMS and TMOS below:

The polymer prepared from the multi-functional linear siloxane compoundof Formula 1 can be easily formed into a ladder structure depending onits structure when polymerized. Accordingly, the polymer can exhibitexcellent physical properties, such as modulus and toughness, and canmaintain its hygroscopicity at a low level. In addition, when thecompound of Formula 7 having a “Q”-shaped structure incorporated in thebackbone chain is polymerized with a siloxane monomer having a ladderstructure, e.g., TS-T4 (OMe), a ladder structure can be easilyintroduced into the polymers to be prepared. The polymers thus preparedhave better physical properties than polymers prepared by conventionalprocesses. In addition, since the polymers are highly compatible withconventional pore-forming materials, they can be very useful in formingdielectric films having low dielectric constants.

When the siloxane compound of Formula 1 is polymerized with at least onecomonomer selected from the compounds of Formulae 8 to 11, the molarratio between the monomers is properly determined according to intendedcharacteristics of the dielectric film to be formed, but there are noparticular limitations on the molar ratio. For example, when the linearsiloxane compound of Formula 1 and another comonomer are polymerized toprepare a copolymer, the molar ratio of the siloxane compound to thecomonomer is between 1:99 and 99:1.

Examples of suitable organic solvents used to prepare the siloxanepolymer of the present invention include, but are not limited to,aliphatic hydrocarbon solvents, such as hexane, heptane, etc.; aromatichydrocarbon solvents, such as anisol, mesitylene, xylene, etc.;ketone-based solvents, such as methyl isobutyl ketone, cyclohexanone,acetone, etc.; ether-based solvents, such as tetrahydrofuran, isopropylether, etc.; acetate-based solvents, such as ethyl acetate, butylacetate, propylene glycol methyl ether acetate, etc.; alcohol-basedsolvents, such as isopropyl alcohol, butyl alcohol, etc.; amide-basedsolvents, such as 1-methyl-2-pyrrolidinone, dimethylacetamide,dimethylformamide, etc.; silicon-based solvents; and mixtures thereof.

Examples of acid catalysts usable in the present invention include, butare not particularly limited to, any acid catalysts which can be used toprepare polysilsesquioxanes, and are preferably hydrochloric acid,nitric acid, benzene sulfonic acid, oxalic acid and formic acid.Examples of base catalysts usable in the present invention include, butare not particularly limited to, any base catalysts that may be used toprepare polysilsesquioxanes, and are preferably potassium hydroxide,sodium hydroxide, triethylamine, sodium bicarbonate and pyridine. Themolar ratio of the total monomers to the catalyst used is in the rangeof 1:1×10⁻⁶ to 1:10. The molar ratio of the total monomers to water isin the range of 1:1 to 1:1000. The hydrolysis and the polycondensationcan be carried out under appropriate time and temperature conditions,and are preferably carried out at 0˜200° C. for 0.1˜100 hours.

The weight average molecular weight of the siloxane polymer ispreferably in the range of 3,000˜300,000, but is not particularlylimited to this range.

Formation of the Dielectric Film

Additionally, the present invention provides a process for forming adielectric film comprising the steps of i) dissolving the siloxanepolymer or copolymer, and if necessary, a pore-forming material toprepare a coating solution; and ii) applying the coating solution onto asubstrate, followed by heat-curing.

Examples of pore-forming materials usable in the present inventioninclude any pore-forming materials that may be used to form porousdielectric films, and are preferably cyclodextrins, polycaprolactones,Brij surfactants, polyethylene glycol-polypropylene glycol-polyethyleneglycol triblock copolymer surfactants and derivatives thereof. Thesecompounds may be used alone or as a mixture of two or more thereof. Thepore-forming material is preferably present in an amount of 0˜70% byweight, based on the total weight of the solid matters (namely, thesiloxane polymer and the pore-forming material) of the coating solution,but is not limited to this range.

Organic solvents usable to prepare the coating solution include, but arenot particularly limited to, all organic solvents described above. Thesolid content of the coating solution is in the range of 0.1˜80% byweight, preferably 5˜70% by weight and more preferably 5˜30% by weight,based on the total weight of the coating solution, but is notparticularly limited to the above ranges. When the solid content is lessthan 0.1% by weight, a film as thin as 1,000 Å or less is undesirablyformed. On the other hand, when the solid content exceeds 80% by weight,the solid matters, particularly the siloxane polymer, may beincompletely dissolved.

It is to be understood that various substrates can be used withoutlimitation so far as they do not detract from the object of the presentinvention. Examples of substrates usable in the present inventioninclude any substrates which are capable of withstanding the heat-curingconditions employed. Glass, silicon wafer and plastic substrates can beused according to the intended application. In the present invention,the application of the coating solution may be carried out by spincoating, dip coating, spray coating, flow coating and screen printingtechniques, but is not especially limited thereto. In view of ease ofapplication and thickness uniformity, the most preferred coatingtechnique is spin coating. Upon spin coating, the coating speed ispreferably adjusted within 800˜5,000rpm.

Optionally, the organic solvent used is evaporated to dry the film afterapplication of the coating solution. The film drying can be conducted byexposing the film to atmosphere, subjecting the film to a vacuum in theinitial stage of the subsequent heat-curing step, or mildly heating thefilm to a temperature of 200° C. or lower.

In step ii), the film is heat-cured at a temperature of 150˜600° C. andpreferably 200˜450° C. for 1˜180 minutes, thereby forming a crack-freeinsoluble coating film. The term “crack-free thin film” as used hereinis defined as a coating film including no cracks when observed by anoptical microscope with a magnification of 1,000×. As used herein, theterm “insoluble coating film” refers to a coating film substantiallyinsoluble in solvents used to deposit the siloxane polymer or solventsknown to be useful in applying a resin onto a substrate. When thecoating solution contains a pore-forming material, the heat-curingtemperature is properly determined considering the decompositiontemperature of the pore-forming material.

Since the dielectric film formed by using the siloxane polymer alone hasa dielectric constant of 3.0 or less, it can be suitable for use as asemiconductor interlayer low dielectric coating film. The dielectricfilm formed by using a mixture of the siloxane polymer and thepore-forming material has a dielectric constant of 2.5 or less. Sincethe dielectric film formed by the method of the present invention hasexcellent mechanical properties, such as toughness and elasticity, and alow carbon content, it can be useful as a semiconductor interlayerdielectric film.

Hereinafter, the present invention will be described in more detail withreference to the following examples. However, these examples are givenfor the purpose of illustration and are not to be construed as limitingthe scope of the invention.

EXAMPLES

First, procedures for measuring the performance of dielectric filmsformed in the following examples are described.

1. Measurement of Dielectric Constant:

First, a thermally oxidized silicon film is applied onto a boron-dopedp-type silicon wafer to a thickness of 3,000 Å, and then a 100 Å-thicktitanium film, a 2,000 Å-thick aluminum film and a 100 Å-thick titaniumfilm are sequentially deposited on the silicon film using a metalevaporator. Thereafter, a dielectric film is coated onto the resultingstructure, after which a 100 Å-thick spherical titanium thin film(diameter: 1 mm) and a 5,000 Å-thick aluminum thin film (diameter: 1 mm)are sequentially deposited on the dielectric film using a hardmaskdesigned to have an electrode diameter of 1 mm, to form a MIM(metal-insulator-metal)-structured low dielectric constant thin film fordielectric constant measurement. The capacitance of the thin film ismeasured at around 10 kHz, 100 kHz and 1 MHz using a PRECISION LCR METER(HP4284A) accompanied with a probe station (Micromanipulatior 6200 probestation). The thickness of the thin film is measured using a prismcoupler. The dielectric constant (k) of the thin film is calculatedaccording to the following equation:k=C×d/∈ _(o) ×Ain which k is the relative permittivity, C is the capacitance of thedielectric film, ∈_(o) is the permittivity of a vacuum (8.8542×10⁻¹²Fm⁻¹), d is the thickness of the dielectric film, and A is the contactcross-sectional area of the electrode.

2. Hardness and Modulus:

The hardness and modulus of a dielectric thin film is determined byquantitative analysis using a Nanoindenter II (MTS). Specifically, afterthe thin film is indented into the Nanoindenter until the indentationdepth reaches 10% of its overall thickness, the hardness and modulus ofthe dielectric thin film are measured. At this time, the thickness ofthe thin film is measured using a prism coupler. In order to securebetter reliability of these measurements in the following Examples andComparative Examples, the hardness and modulus are measured at a totalof 9 indention points on the dielectric film, and the obtained valueswere averaged.

3. Carbon Content:

In the following Examples and Comparative Examples, the carbon contentof dielectric films is measured by XPS (X-ray photoelectronspectroscopy) using a Q2000 (Physical Electronics). As an X-raygenerating apparatus, a monochromatic Al source (1486.6 eV) is used.Specifically, after the thin films are sputtered using Ar ions at 3 keV,element quantitative analysis is performed at each depth. Valuesmeasured at a certain depth where the content of each element wasmaintained to be constant were averaged, and the obtained average valuewas determined as a carbon content.

Synthesis of Monomers

1) Synthesis of Multi-Functional Linear Siloxane Monomer (L5):

0.444 moles (17.767 g) of sodium hydroxide and 200 ml of tetrahydrofuran(THF) are placed in a reaction flask. After the mixture is cooled to 0°C., 1.3 moles (200 ml) of vinyltrimethoxysilane is added thereto. Thetemperature of the reaction mixture is gradually raised to roomtemperature. At this temperature, the reaction is allowed to proceed for12 hours. Volatile materials are completely evaporated at a pressure ofca. 0.1 torr to obtain sodium silanolate as a solid. The solid salt isdissolved in 800 ml of THF. After the resulting solution is cooled to 0°C., 40 g of dichlorodiethoxysilane (purity: 90%, Gelest Co.) is slowlyadded thereto. After completion of the addition, the mixture is reactedat room temperature for 12 hours. The reaction mixture is evaporated ata pressure of ca. 0.1 torr to remove volatile materials, dissolved in800 ml of hexane, and filtered through celite. Hexane is removed bydistillation at reduced pressure to afford a liquid compound representedby the following formula:

[1H NMR (300 MHz) data (CDCl₃): δ 1.17˜1.21 (t, 6H, —O—C—CH₃), 3.53 (s,12H, 4×OCH₃), 3.78˜3.82 (q, 4H, 2×—OCH₂—), 5.85˜6.08 (m, 6H,2×—CH═CH₂)].

0.11 moles (41.85 g) of the liquid compound and a solution of 0.46 g ofplatinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex in xyleneare charged into a flask, and then the resulting mixture is diluted in300 ml of THF. To the dilution is slowly added 0.33 moles (40.3 g) oftrimethoxysilane. The reaction is continued at 50° C. for 48 hours.After the reaction solution is cooled to room temperature, volatilematerials are completely evaporated at a pressure of ca. 0.1 torr. 300ml of hexane and log of activated carbon are added to the concentrate.After the resulting mixture is stirred for 6 hours, it is filteredthrough celite. Hexane is removed by distillation at a pressure of 0.1torr to afford 60.4 g (yield: 87.9%) of the multi-functional linearsiloxane compound L5 represented by the following formula:

[1H NMR (CDCl₃) (300 MHz) data: δ 0.52˜0.64 (m, 5.7H of 8H, —CH₂CH₂— and—Si—CH—Si—, kinetic product), 1.13˜1.22 (t, 6H, —O—C—CH₃), 1.13˜1.22 (d,2.3 H of 8H, —Si—CCH₃—Si—, thermodynamic product), 3.53 (s, 30H,10×OCH₃), 3.80˜3.87 (q, 4H, 2×—OCH₂—)]

2) Synthesis of Multi-Functional Linear Siloxane Monomer (L6):

A solution of 7.27 mmol (1.29 g) of palladium (II) dichloride [PdCl₂(II)] in 30 ml of carbon tetrachloride is placed in a flask, and then0.106 moles (24 g) of 1,1,1,3,3-pentamethoxy-1,3-disilapropane (98%,Korea Institute of Science and Technology (KIST)) is slowly addedthereto at 0° C. The reaction is allowed to proceed at this temperaturefor 4 hours. The reaction mixture is filtered through celite to obtain3-chloro-1,1,1,3,3-pentamethoxy-1,3-disilapropane.

Thereafter, 0.12 moles (2.88 g) of sodium hydroxide and 200 ml oftetrahydrofuran are charged into the flask. After the temperature of theflask is lowered to 0° C., 0.31 moles (45 ml) of methyltrimethoxysilaneis added thereto. The mixture is slowly warmed to room temperature. Thereaction is further continued for 12 hours. Thereafter, volatilematerials are completely evaporated at a pressure of ca. 0.1 torr toobtain sodium silanolate as a solid. The solid salt is dissolved in 200ml of THF. After the resulting solution is cooled to 0° C., the3-chloro-1,1,1,3,3-pentamethoxy-1,3-disilapropan previously preparedabove is slowly added thereto. After completion of the addition, thereaction is continued at room temperature for 12 hours. The reactionmixture is evaporated at a pressure of ca. 0.1 torr to remove volatilematerials, dissolved in 200 ml of hexane, and filtered through celite.Hexane is removed by distillation at reduced pressure to afford 28.5 g(yield: 77.5%) of liquid compound L6 represented by the followingformula:

[1H NMR (CDCl₃) (300 MHz) data: δ 0.14˜0.03 (m, 5H, 1×CH₂ and 1×CH₃),3.50 (s, 21H, 7×OCH3)]

3) Synthesis of Comonomer TS-T4 (OMe):

A solution of 40 mmol (7.09 g) of palladium (II) dichloride [PdCl₂ (II)]is dissolved in 70 ml of carbon tetrachloride, and then 0.1442 moles (35ml) of 2,4,6,8-tetramethyl-2,4,6,8-cyclotetrasiloxane is slowly addedthereto at 0° C. The reaction is allowed to proceed at this temperaturefor 4 hours. The reaction mixture is filtered through activated carbonand celite. The obtained filtrate is diluted in 700 ml of THF, and then0.631 moles (88 ml) of triethylamine is added thereto. After theresulting mixture is cooled to 0° C., 0.69 moles (28 ml) of methanol isslowly added thereto. The temperature is raised to room temperature, andthe reaction is continued for 15 hours. The reaction mixture is filteredthrough activated carbon and celite. Volatile materials are removed bydistillation at reduced pressure (ca. 0.1 torr) to afford liquid monomerTS-T4 (OMe) represented by the following formula:

The analytical results of the ¹H-NMR spectrum (300 MHz) of the monomerare as follows: δ 0.067 (s, 12H, 4×[—CH₃]), 3.55 (s, 3H, 4×[—OCH₃]).

4) Synthesis of Comonomer TCS-2:

29.01 mmol (10.0 g) of2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane and a solutionof 0.164 g of platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxanecomplex in xylene are charged into a flask, and then the resultingmixture is diluted in 300 ml of diethyl ether. After the reactionsolution is cooled to −78° C., 127.66 mmol (17.29 g) of trichlorosilaneis slowly added thereto. After the temperature of the flask is graduallyraised to room temperature, the reaction is allowed to proceed for 40hours. The reaction solution is concentrated at reduced pressure (ca.0.1 torr) to remove volatile materials. 100 ml of hexane is added to theconcentrate. After the resulting mixture is stirred for 1 hour, it isfiltered through celite. Hexane is removed by distillation at a pressureof ca. 0.1 torr to obtain a liquid reaction product.

11.56 mmol (10.0 g) of the liquid reaction product is diluted in 50 mlof THF, and then 138.71 mmol (13.83 g) of triethylamine is addedthereto. The reaction temperature is lowered to −78° C. After 136.71mmol (4.38 g) of methanol is slowly added to the solution, the reactiontemperature is slowly raised to room temperature. The reaction isallowed to proceed for 15 hours. The reaction mixture is filteredthrough celite. The obtained filtrate is concentrated at reducedpressure (ca. 0.1 torr) to remove volatile materials. After 100 ml ofhexane is added to the concentrate, the resulting mixture is stirred for1 hour, filtered through celite, and then 5 g of activated carbon isadded thereto. After the mixture is stirred for 10 hours, it is filteredthrough celite. Hexane is removed by distillation at reduced pressure(ca. 0.1 torr) to afford colorless liquid monomer TCS-2 represented bythe following formula:

The analytical results of the ¹H-NMR spectrum (300 MHz, acetone-d₆) ofthe monomer are as follows: δ 0.09 (s, 12H, 4×[—CH₃]), 0.52˜0.64 (m,16H, 4×[—CH₂CH₂—]), 3.58 (s, 36H, 4×[—OCH₃]₃).

Preparation of Copolymers

As shown in Table 1 below, the multi-functional linear siloxane monomersL5 and L6 prepared in Preparative Examples 1) and 2), and TS-T4 (OMe)and TCS-2 prepared in Preparative Examples 3) and 4), respectively, andcommercially available MTMS (methyltrimethoxy silane, Sigma Aldrich) ascomonomers are used to prepare polymers (a) to (i). For the purpose ofcomparison, TCS-2 and MTMS are used to prepare polymer (j).

The respective copolymers were prepared in accordance with the followingprocedure. First, selected monomers are charged into a flask, and arethen diluted in THF in the amount of 12 times the amount of monomersused. After the temperature of the dilution is lowered to −78° C., HCland water are added to the dilution. At an elevated temperature of 70°C., the reaction is allowed to proceed for 12 hours. The reactionsolution is transferred to a separatory funnel, followed by addition ofdiethylether in the same amount as that of THF. The resulting mixture iswashed three times with water in the amount of about one tenth of thetotal volume of the solvents used, and is then distilled at reducedpressure to remove volatile materials, yielding a corresponding polymeras a white powder. The polymer is dissolved in tetrahydrofuran until itis transparent, and filtered through a filter (pore size: 0.2 μm). Wateris added to the filtrate to obtain a white precipitate. The precipitateis dried at 0˜20° C. and 0.1 torr for 10 hours to afford a correspondingsiloxane polymer.

TABLE 1 Monomers (mmol) HCl H₂O Amount of Polymer L5 L6 TS-T4 (OMe)TCS-2 MTMS (mmol) (mmol) Polymer (g) (a) 6.61 6.61 1.059 353 3.52 (b)4.77 9.54 0.954 318 3.27 (c) 6.56 9.84 1.181 393 3.06 (d) 7.80 2.601.040 346 2.55 (e) 8.02 8.02 1.203 180 2.90 (f) 7.95 18.5 1.510 227 3.82(g) 5.57 50.1 2.170 724 3.27 (h) 20.2 20.2 2.060 688 6.02 (i) 5.61 5.611.062 354 2.10 (j) 4.80 43.2 1.872 629 5.93Formation of Dielectric Films

As shown in Table 2 below, the respective dielectric films are formed inaccordance with the following procedure. First, the siloxane polymer andheptakis(2,3,6-tri-methoxy)-β-cyclodextrin as a pore-forming materialare used to prepare a thin film composition. The composition isdissolved in propyleneglycol methyletheylether acetate to prepare acoating solution. When the siloxane polymer alone is used to form adielectric film, the solid content is fixed to 25% by weight. On theother hand, when the polymer and the pore-forming material are used, thesolid content is fixed to 27% by weight. The coating solution isspin-coated on a silicon wafer at 3,000 rpm for 30 seconds, andpre-baked on a hot plate under nitrogen atmosphere at 150° C. for 1minute and at 250° C. for 1 minute, sequentially. The pre-baked siliconwafer is dried to form a film. The film is baked under a nitrogenatmosphere while heating to 420° C. for 1 hour at a rate of 3° C./min.).

The thickness, refractive index, dielectric constant, hardness, modulusand carbon content of the dielectric films thus formed are measured. Theresults are shown in Table 2 below.

TABLE 2 Composition of coating solution Pore- Dielectric Siloxaneforming Carbon film polymer material Thickness Refractive DielectricHardness Modulus content Nos. (wt %) (wt %) (Å) index constant (GPa)(GPa) (%) A (a) 100 — 8595 1.410 3.11 1.87 10.54 19.62 A-1 (a) 70 307990 1.297 2.17 0.65 4.00 17.05 B (b) 100 — 9976 1.406 3.04 1.50 8.6918.38 B-1 (b) 70 30 9133 1.296 2.21 0.50 3.07 16.41 C (c) 100 — 86271.4217 2.68 1.76 9.69 16.52 C-1 (c) 70 30 8682 1.306 2.28 0.65 3.9912.08 F (f) 100 — 9129 1.420 3.42 2.21 12.78 21.05 F-1 (f) 70 30 93891.301 2.30 0.80 5.16 16.61 G (g) 100 — 6184 1.405 2.82 1.67 9.47 19.21G-1 (g) 70 30 6431 1.302 2.15 0.73 4.23 17.83 H (h) 100 — 10888 1.4103.74 2.17 13.06 16.36 H-1 (h) 70 30 11221 1.276 2.12 0.66 4.22 11.78 I(i) 100 — 14213 1.425 — 1.52 8.29 24.30 I-1 (i) 70 30 10258 1.318 2.230.59 3.43 21.67 J (j) 100 — 11654 1.415 2.70 1.13 5.90 29.0 J-1 (j) 7030 9811 1.335 2.24 0.50 2.86 25.6

As can be seen from Table 2, the dielectric films formed by using thecopolymers prepared from the multi-functional linear siloxane monomer L5or L6 exhibited a similar dielectric constant, but a high hardness, ahigh modulus and a low carbon content, compared to the dielectric filmformed by using the copolymer prepared from previously known TCS-2 andMTMS. Accordingly, the dielectric films are advantageously applicable tosemiconductor processes.

As apparent from the above description, the siloxane compound of thepresent invention is highly reactive. In addition, the siloxane polymerprepared from the siloxane compound not only has satisfactory mechanicalproperties, thermal stability and crack resistance, but also exhibits alow hygroscopicity and excellent compatibility with pore-formingmaterials, which leads to a low dielectric constant. Furthermore, thesiloxane polymer retains a relatively low carbon content but a high SiO₂content, resulting in its improved applicability to semiconductorprocesses. Therefore, the siloxane polymer can be advantageously used asa material for dielectric films of semiconductor devices.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the spirit and scope of the inventionas disclosed in the accompanying claims.

1. A multi-functional linear siloxane compound represented by any one ofFormulae 5 to 7 below: